To document that calcium-regulated PTH release is indeed abnormal in patients with primary hyperparathyroidism, dynamic tests of parathyroid gland function will be done using the four-parameter model developed by Brown and colleagues in subjects with established primary hyperparathyroidism (14, 15). The specific aim of this study is to determine the set point for calcium-regulated PTH release in patients with primary hyperparathyroidism compared to normal adult volunteers.